Highly reactive metal hydrides, process for their preparation and use

ABSTRACT

The invention relates to powdery, highly reactive alkali and alkaline earth hydride compounds, and to mixtures with elements of the third main group of the periodic table of elements (PTE) and to the preparation thereof by reacting alkali or alkaline earth metals in the presence of finely dispersed metals or compounds of the third main group of the PTE, wherein the latter have one or more hydride ligands or said hydride ligands are converted in situ, under the prevailing reaction conditions, i.e., in the presence of hydrogen gas or another H source, into hydride species, and to the use thereof for the preparation of complex hydrides and organometallic compounds.

The subject matter of the present patent specification relates to apowdery, highly reactive alkali and alkaline earth hydride compounds andto mixtures with elements of the 3rd main group of the periodic table ofelements (PTE) and to the preparation thereof by reacting alkali oralkaline earth metals in the presence of finely dispersed metals orcompounds of the third main group of the PTE, wherein the latter haveone or more hydride ligands or said hydride ligands are converted insitu, under the prevailing reaction conditions, i.e., in the presence ofhydrogen gas or another H source, into hydride species, and to the usethereof for the preparation of complex hydrides and organometalhydrides.

The hydrides of the metals of the 1st and 2nd group of the PTE belong tothe salt-type ionic compounds and are prepared as a rule by reacting themetal in question with hydrogen at elevated temperatures and underhydrogen atmosphere (P. Rittmeyer, U. Wietelmann, Ullmann's Encyclopediaof Industrial Chemistry, VCH Weinheim, Vol. A 13, 1989). Thus, thehighly stable lithium hydride is synthesized at 700-900° C. under 1 barhydrogen atmosphere in the melt. After the completed reaction, the meltis cooled and the solidified hydride is broken and ground. Sodiumhydride is also produced in the molten state in a high boiling oil at250-300° C. under hydrogen. Magnesium hydride is synthesized frompowdery magnesium at 300-400° C. under an H₂ pressure of 100-150 bar.

The metal hydride powders prepared in this manner have a relatively lowreactivity, i.e., they have only relatively low alkaline properties (P.A. A. Klusener, L. Brandsma, H. D. Verkruijsse, P. v. Rague Schleyer, T.Friedl, R. Pi, Angew. Chem. 98 (1986), 458-9) and they are not suitableor poorly suitable, for example, for the hydride transfer on Lewis acidsof the type R3B (R=sterically hindered alkyl groups, for example,sec-butyl). This applies particularly to lithium hydride. To be able touse commercial lithium hydride, for example, for the preparation oflithium tri-sec-butylborohydride from tri-sec-butylborane (B(secBu)s), acatalyst is needed, for example, a metal amino borohydride. However, atroom temperature (RT), relatively long reaction times (EP 1272496 B1,700 minutes, see Example 5) are necessary for a completed reaction.Moreover, it is known to prepare alkali metal triple alkyl-substitutedborohydride compounds M[R¹R²R³BH] from an alkali metal, a hydrogen donorand a triple alkyl-substituted borane. The hydrogen donor is preferablyselected from the group consisting of hydrogen, deuterium, tritium,ether, cyclohexadiene, cyclohexene. In the case of an alkali metal,except for potassium, the presence of a transition metal catalyst (forexample, FeCb) and/or of a polycyclic aromatic compound (for example,naphthalene, phenanthrene) is necessary (U.S. Pat. No. 5,886,229). Here,it is disadvantageous that the solution of product formed iscontaminated by these catalysts or the degradation products thereof.

Moreover, highly reactive alkali metal hydride reagents (MH_(n)*) havebeen reported to be quite usable for metalation reactions. The highlyreactive variant of the respective metal hydride (MH_(n)*) or metal(M²*) is marked using superscript asterisks (“*”). The preparation ofsuch reagents was described for M=Li in a review article (U. Wietelmann,Lithium Hydride, Lithium Halides, LiO and LiS-Compounds, Science ofSynthesis (Houben-Weyl, Methods of Molecular Transformations), Vol. 8,chap. 8.1.2 - 8.1.5, 2006). As a rule, the preparation of such reactivehydride species starts with expensive raw materials (for example,butyllithium-n-BuLi in N,N,N′,N′-tetramethylethylenediamine—TMEDA),wherefore such products have no commercial relevance. The most importantpreparation route consists of the hydrogenolysis of n-BuLi/TMEDA bymeans of hydrogen or 1,3-cyclohexadiene (P. A. A. Klusener, L. Brandsma,H. D. Verkruijsse, P. v. Rague Schleyer, T. Friedl, R. Pi, Angew. Chem.98 (1986), 458-9):

C₄H₉Li/TMEDA+H₂→C₄H₀+LiH^(x)j+TMEDA   (1)

Moreover, there is a report on the synthesis of active alkali metalhydride compounds of the elements Li, Na and K by reacting alkali metalin pieces in tetrahydrofuran (THF) at 40° C. in the presence of acatalyst combination consisting of a transition metal compound, forexample, TiCl₄ and naphthalene under hydrogen atmosphere (Y. Zhang, S.Liao, Y. Xu, J. Mol. Cat. 84 (1993) 211-221). The NaH* produced in thismanner could be used for the dehalogenation of bromobenzene and chloridebenzene in boiling THF. Moreover, in the presence of various transitionmetal catalysts, LiH* and NaH* can be used for reducing hexene tohexane. The disadvantage of the last-mentioned synthesis variant is thatthe synthesis mixtures formed are contaminated with a combination oftransition metals and naphthalene.

Since commercial magnesium hydride is insufficiently reactive to beusable for syntheses of, for example, dialkyl magnesium compounds byhydromagnesation of olefins, attempts have been made to prepare it in amore reactive form. Active magnesium hydride can be prepared byhigh-pressure hydrogenation of Grignard compounds at higher temperatures(71-150° C., 350 bar) according to

2RMgX+2H₂→2RH+MgX₂+MgH₂*   (2)

(W. E. Becker, E. C. Ashby, J. Org. Chem. 29, 954 (1964)). In a similarmanner, dialkylmagnesium compounds, for example, dibutylmagnesium, canalso be converted by high-pressure hydrogenolysis (5 MPa) at 200° C.into MgH₂* (E. J. Setijadi, C. Boyer, Phys. Chem. Chem. Phys. 2012, 14,11386-97). Due to the unfavorable conditions, the expensive Mg sources,and, in the case of the Grignard compounds, the unavoidablecontamination with magnesium halides (MgX₂), this MgH₂* formation methodhas not gained importance.

Moreover, a method has been described for preparing highly reactivemagnesium hydride by hydrogenation of Mg metal in a THF suspension andin the presence of a chromium-containing homogenous catalyst (B.Bogdanovic, P. Bons, S. Konstantinovic, M. Schwickardi, U. Westeppe,Chem. Ber. 1993, 126, 1371-83; US 4554153 A1). The THF-soluble catalystconsists of a CrCl₃/Mg-anthracene complex. The hydrogenation runs onlyunder high-pressure conditions (for example, 80 bar). The activemagnesium hydride MgH₂* prepared in this manner is reacted with anolefin in the presence of a transition metal catalyst, which is ahalogen compound of metals of subgroups IV to VIII of the PTE,preferably in THF in the temperature range of 0 to 200° C. and at apressure of 1 to 300 bar. According to the document EP 0014983 B 1,dialkylmagnesium compounds are obtained with moderate to very goodyields as solutions in THF. Due to the use of toxic chromium compoundsand the necessarily high hydrogen pressures in the MgH₂* preparation,this synthesis variant is also disadvantageous.

From the document EP 514707 B 1, another process is known, in whichmagnesium hydride is activated, before or during the reaction with anolefin, by grinding to a particle size of ≤10 μm, preferably ≤1 μmwithout the addition of complex catalysts. In the reaction with theolefin in an ether solvent, preferably THF or diglyme, a transitionmetal halide according to EP 0014983 B1 is added as catalyst. Thedisadvantage is that the yields of dialkylmagnesium compounds are as arule low (25-34%).

The object of the invention is to indicate a process which, startingwith inexpensive, commercially available raw materials, under mildconditions and without the use of toxic transition metal catalysts (forexample, chromium), enables the synthesis of reactive metal hydrides(MH_(n)*) of the 1st and 2nd group of the periodic table. In addition,the hydrides should be produced as directly as possible in a form usefulfor synthesis purposes (i.e., as powder or dispersions in a solvent) andhave a sufficiently high reactivity so that they have a broad synthesisapplication range, that is to say they are capable of

addition to Lewis acids such as trialkylboranes

addition to olefinic compounds (also for hydrometalation), and

deprotonation of acid compounds (for example, CH acids).

According to the invention, the object is achieved in that metals M ofthe first or second period of the PTE are reacted with a compound ofgeneral formula M¹ _(x)[M²H_(3+x)]_(b) under inert gas (preferably argonaccording to Eq. 3) or optionally in the presence of hydrogen gas oranother source of hydrogen, and in the presence of a finely dispersedreactive metal of the third main PTE group (M²* ) or of a compound withthe more broadly written general formula M¹ _(x)[M²(A¹ _(y)A²_(z))_(3+x)]_(b) according to (aq. 4)

Here:

M¹=an alkali metal (Li, Na, K, Rb, Cs), an alkaline earth metal (Be, Mg,Ca, Sr, Ba) or (applicable only to Eq. 4) an element from the group ofthe rare earths (Sc, Y, La, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, Lu);

x=0 or 1;

M²=an element of the 3rd main group of the PTE selected from the B, Al,Ga, In;

n=1 or 2, corresponding to the valence of the metal M;

b=the valence of M¹.

Moreover, in the case of equation (3):

m=1 or 2, corresponding to the valence of the metal M¹;

and in the case in which x=0, p=0, and

for M=alkali element, o and q=2, and

for M=alkaline earth element, o and q=4;

in the case in which x=1:

for M and M¹=alkali metals, the factors o, p, q=2;

for M and M¹=alkaline earth metals, the factors o, p=1, and q=2;

for M=alkali metal and M¹=alkaline earth metal, the factors o, p=2 andq=4, and

for M=alkaline earth metal and M¹=alkali metal, the factors o, p, q=4.

In addition, for equation (4):

A¹=H or an alkyl group containing 1-18 C atoms, wherein the up to four Agroups can be identical or different;

A²=an alkoxy residue (OR with R=alkyl with 1-8 C atoms), a dialkylaminoresidue (NR₂ with R=alkyl with 1-8 C atoms) or a halogen from Cl, Br, I,and

y can assume the value 1, 2 or 3, wherein y+z=3.

In the absence of a hydrogen source, A¹ and A² can only mean H, i.e.,the reaction occurs exclusively according to Eq. (3). A suspension thenforms, which contains a highly reactive metal hydride MH_(n)* in themixture with q/6 equivalents (eq.) of highly reactive metal M²* and p/6of highly reactive metal hydride M¹H_(m)*. If, for the subsequentreactions (Eq. 7-9), pure metal hydride products, i.e., metal hydrideproducts containing only a metal cation (except for the metal M²), aredesirable, it is preferable that M¹ and M are identical. For example,the combinations LiAlH₄ and Li or NaAlH₄ and Na are particularlypreferable. For the case in which x=0, which is also particularlypreferable, one necessarily obtains, with regard to the cation, directlypure metal hydride products MH_(n)*. As an example for a particularlypreferred combination, the preparation of active lithium hydride,LiH^(*), using LiAlH₄, is shown:

3Li+LiAlH₄−>4LiH*+Al*

Under hydrogen atmosphere, LiAlH₄ can be used in catalytic quantities:

The mixtures of highly reactive metal M^(2*) and of the highly reactivemetal hydride MH_(n)*, which are prepared according to the invention,can be used directly as suspensions for subsequent reactions. It is alsopossible to remove the solvent largely or completely and thus preparehighly reactive powdery mixtures of M^(2*) and MH_(n)*. Thesolvent-free, highly reactive products, when in contact with air, turnout to be pyrophoric and consequently have to be handled exclusively ina vacuum or under inert gas conditions (preferably under argon).

Reaction equation (4) applies to the case of an approximatelystoichiometrically introduced hydrogen quantity; in the case of ahypostoichiometric reaction procedure or in the case of insufficientlylong reaction times, elemental or only partially hydrogenated metal M²can remain. In the presence of elemental hydrogen or a source forhydrogen, the compound M¹ _(x)[M²(A¹ _(y)A² _(z))_(3+x)]_(b) is neededonly in catalytic quantities. The compound M¹ _(x)[M²(A¹ _(y)A²_(z))_(3±x)]_(b) is used in catalytic quantities from 0.001 to 20 mol %,preferably from 0.01 to 10 mol %, with respect to the metal M. Under therespective reaction conditions, it can be converted into a relatedspecies. For example, if AlH₃ is used, then, after the reactionaccording to (4) has taken place in the presence of equimolar or excessH₂ quantities, M[AlH₄]_(n) can be present. However, if elemental M isstill present (meaning that, for example, due to a lack of H₂, not allthe M has been converted to MH_(n)*), the aluminum introduced in theform of AlH₃ will be at least partially in elemental form.

It is also possible to achieve the desired metal hydride formation inthe presence of the elemental metal M² and hydrogen, wherein M² is usedin catalytic quantities from 0.001 to 20 mol %, preferably from 0.01 to10 mol %, with respect to the metal M:

This reaction procedure requires the use of a highly reactive metalgrade M²* , preferably finely dispersed or amorphous aluminum. Thehighly reactive M² must have a mean particle size D₅₀ between 0.01 and100 μm and it must not be affected by previous contact with air, oxygen,moisture and other reactive substances with regard to its reactivity.Alternatively, an industrial available metal grade, for example,aluminum metal powder or aluminum metal shavings, can also be used.However, such materials are not easily hydrogenated and require theaddition of transition metal catalysts (for example, Ti, V, Fe) and/orhigh H₂ pressures (at least 10, preferably at least 50 bar). Since veryfine/amorphous metal powders are not commercially available andhigh-pressure installations are relatively cost intensive, this variantis less preferable. It is thus simpler and more cost effective to use,as hydrogen transfer auxiliaries, the compounds represented by thegeneric formula M¹ _(x)[M²(A¹ _(y)A² _(z))_(3+x)]_(b) in catalyticquantities.

It was found surprisingly that the hydrogenation of M in the presence offinely dispersed, highly reactive metal M^(2*) and/or compounds ofgeneral generic formula M¹ _(x)[M²(A¹ _(y)A² _(z))_(3+x)]_(b) underhydrogen atmosphere or in the presence of another hydrogen sourcesucceeds under mild conditions with high yield. The prerequisite is thatthe metal M has a more negative standard potential than the metal M².Below, the respective standard potentials are compiled (D. R. Lide,Handbook of Chemistry and Physics 83^(rd) ed., 2002-2003):

1st main Normal 2nd main Normal 3rd main Normal group potential grouppotential group potential M = (V) M = (V) M² = (V) Li −3.0401 Be −1.847B no value Na −2.71 Mg −2.372 Al −1.662 K −2.931 Ca −2.868 Ga −0.539 Rb−2.98 Sr −2.899 In −0.3382 Cs −3.026 Ba −2.912

It is assumed that the hydrogen of M²-H compounds is transferred to thebase metals M and that the driving force of the reaction consists in theformation of the thermodynamically more stable hydride(s). Due to thedehydrogenation of M¹ _(x)[M²(A¹ _(y)A² _(z))_(3+x)]_(b), elemental M²*forms; the latter is present in an extremely reactive (finelydispersed,: in part amorphous form), and it is very reactive withrespect to, for example, hydrogen, i.e., it is rehydrogenated in thepresence of the metal M and of a hydrogen source. On this backdrop, itis understandable that the use of M¹ _(x)[M²(A¹ _(y)A² _(z))_(3+x)]_(b)or of highly reactive/activated elemental M^(2*) in catalytic quantitiesis sufficient.

As stoichiometric hydrogenation agents or hydrogenation catalysts, it ispreferable to use compounds of aluminum M¹ _(x)[Al(A¹ _(y)A²_(z))_(3+x)]_(b) or highly reactive/activated aluminum metal Al*. Inparticular, the alkali alanates LiAlH₄ and NaAlH₄, which are prepared onthe industrial scale, are particularly suitable. Alane AlH₃ can also beused with equal success.

It was surprisingly found that certain non-hydride compounds of generalformula M¹ _(x)[M²(A¹ _(y)A² _(z))_(3+x)]_(b) can also be used (thussuch compounds in which neither A¹ nor A²=H), when the hydrogen issupplied in elemental form (H₂) or in molecularly stored form (forexample, as 1,3-cyclohexadiene). Without being bound to the correctnessof the hypothesis, it is assumed that, under hydrogenation conditions, areactive form of the metal M^(2*) or an alloy consisting of M^(2*) and Mforms, which can take up hydrogen and transfer it in a subsequent stepto the base metal M. This is explained using the example of theindustrially available aluminum alkyls (that is to say, M²=Al). Forexample, if triethylaluminum is reacted with elemental lithium in a THFsuspension, then the formation of black, finely dispersed aluminum isobserved, while the lithium dissolves at least partially:

4Et₃Al+3Li→3LiAlEt₄+Al*↓   (6)

Et₃Al+3Li→3LiEt+Al*↓   (6a)

LiEt+Et₃Al→LiAlEt₄   (6b )

The finely dispersed Al* or a forming reactive Al alloy reacts readilywith hydrogen to form aluminum-containing hydrides, for example, AlH₃.The latter in turn can transfer the hydrogen under mild conditions tobase metals M. Similarly, by the reaction of AlCl₃ in ether solutions byreaction with, for example, lithium metal, reactive elemental aluminummetal forms in addition to LiAlCl₄. The aluminates such as Li[AlEt₄] canreact with hydrogen to form hydride-containing species.

The hydrogenation of the metals M according to equations (3) - (5) iscarried out preferably in the presence of an anhydrous organic solvent.Suitable as such a solvent are ethers (open-chain or cyclic, such asdiethyl ether, 1,2-dimethoxyethane, diethylene glycol dimethyl ether,tetrahydrofuran, 2-methyl tetrahydrofuran, tetrahydropyrane, dioxane,dioxolane and others), tertiary amines (triethylamine, tributylamine,morpholine, etc.), hydrocarbons (saturated C₄-C₁₈, preferably pentanes,hexanes, heptanes, octanes, etc.; aromatic compounds such as benzene,toluene, ethylbenzene, xylenes, cumene, etc.) in pure form or as anymixtures of at least two of the solvents listed. However, in principleit is also possible to carry out the hydrogenations without solvent.Thus, a liquid K/Na alloy already reacts at room temperature withcomplex alanates, for example, LiAlH₄. However, since such a reactionprocedure is difficult to control, this process variant is lesspreferable.

The reaction temperatures can vary within broad limits, as a rule theyare between −20 and 150° C., preferably 0 and 100° C., and particularlypreferably between 25 and 70° C. If a reaction procedure according to(4) or (5) is intended, then contact with elemental hydrogen must beensured. Frequently an unpressurized mode of operation is sufficient;however, in order to achieve the shortest reaction times possible, it ispossible to work under H₂ pressure conditions. Preferably, the H₂ excesspressure is 2-300 bar, particularly preferably 10-100 bar. It is alsopossible to use, as hydrogen source, a compound which releases hydrogenunder selected operating conditions. Examples of this are:1,3-cyclohexadiene, decalin, N-ethylcarbazole.

As hydrogenation auxiliaries M¹ _(x)[M²(A¹ _(y)A² _(z))_(3+x)]_(b),metal hydride aluminates, for example, LiAlH₄, NaAlH₄, KAlH₄ and/oralane AlH₃ are preferably used. However, mixed alanates such asNa[H₂Al(O(CH₂)2OCH₃)₂], Na[H₂Al(C₂H₅)₂] or mixed alanes such asHAl(C₄H₉)₂ or H₂AlC₄H₉ can also be used. In the presence of anindependent hydrogen source, trialkylalanes such as Al(CH₃)₃, Al(C₂H₅)₃,Al(C₄H₉)₃, sesquialanes such as Et_(3−x)AlCl₃ (x=1 to 3) or aluminumhalides such as AlCl₃ or AlBr₃ are suitable.

The products according to the invention are produced in finelydispersed, in part nano-scale form. They are extremely reactive withrespect to air and water, frequently even pyrophoric (i.e., they ignitespontaneously when air enters). Consequently, they have to be handledand stored with exclusion of reactive gases, i.e., in a vacuum, undernitrogen or inert gas atmosphere. The products according to theinvention consist mainly of the highly reactive metal hydride MH_(n)*and, depending on reaction management (Eq. 3 or 4 or an intermediatecase), they contain different quantities of M²* and M¹H_(m)*. The molarratio between MH_(n)*, M²* and M¹H_(m)* is 1:0.001 to q/6:0 to p/6,preferably 1:0.01 to q/6:0 to p/6.

In a particularly preferred embodiment type, the metal hydrogenationsare carried out according to Equations (3)-(5) in the presence of Lewisacids or unsaturated compounds that can be hydrometalated. Thesecompounds are subsumed below under the term MH_(n)* acceptors.

In this manner, selectively acting metal hydride reagents ororganometallic compounds of the metals M, usable, for example, forsynthesis purposes, can be obtained directly and conveniently. Inaddition, one avoids the manipulation and isolation of the extremelysensitive pyrophoric metal hydride solid substances. The followingreaction diagrams can be used as examples of such a reaction procedure:

The residues R, R¹, R², R³, R⁴ are any unbranched, cyclic or branchedalkyl groups containing 1 to 12 C atoms.

As MH_(n)* acceptors the following compounds can be used above all:

preferable raw materials R3B for (Eq. 7) are: tri-sec-butylborane,trisiamylborane, tricyclohexylborane,

preferred raw materials Al(OR)3 for (Eq. 8) are: aluminum trimethylate,aluminum tri(tert-butylate), aluminum tri(tert-pentylate), and

preferred olefins for (Eq. 9) are olefins with R¹, R² and R³=H, i.e.,a-olefins, particularly preferably 1-propene, 1-butene, 1-pentene,1-hexene, 1-heptene, 1-octene. Moreover, olefins with R² and R⁴=alkylgroups containing 1-12 C atoms can be used. Under certain conditions,olefins with internalized double bonds, for example, 2-butene,2-pentene, 2-hexene, 2-heptene, 2-octene, 2-decene can also be accessedby the hydrolithiation reaction according to the invention.

For carrying out the in situ utilization reactions of the highlyreactive metal hydrides MHn*, several particular process variants exist,for example:

Variant A: the MH_(n)* acceptor is added partially or completely beforethe start of the metal hydride formation to the mixture of the metalpowder M and an aprotic solvent or solvent mixture. Then, the reagent M¹_(x)[M²(A¹ _(y)A² _(z))_(3+x)]_(b) used for the H transfer is added instoichiometric quantity or as a catalyst. In the latter case, thereaction mixture is moreover brought in contact with a hydrogen source,most simply with elemental hydrogen.

Variant B: the highly reactive metal hydrides MH_(n)* are formedpartially or completely according to reaction equations (2)-(4), and itis only then that the MH_(n)* acceptor is added.

The hydrometalation reaction according to Eq. (9) can be accelerated bythe addition of catalytically active transition metal compounds. Ascatalysts, the halogen or alkoxy compounds of the 4th and 5th subgroupof the PTE can be considered, in particular the chlorides of Ti, Zr, Hf,V, Nb, Ta, preferably TiCl₄, ZrCl₄ and VCl3, as well as metallocenecompounds of the mentioned metals such as, for example, Cp₂TiCl₂,CpTiCl₃, Cp₂ZrCl₂, or other complex compounds of the mentioned metals.They are added in quantities from 0.001 to 10 mol %, preferably 0.005 to5 mol % with respect to metal hydride MH_(n)*.

The invention is explained based on the following examples.

EXAMPLE 1 Preparation of Active Lithium Hydride LiH* from LiAlH₄ andLithium Powder in THF

In a glass flask rendered inert (i.e., heated and filled with argon),0.29 g (41.8 mmol) of lithium powder (D₅₀=approximately 80 μm) weresuspended in 50 mL of dry tetrahydrofuran. Then, 13.9 mmol LiAlH₄ in theform of an approximately 10% solution in tetrahydrofuran were added bymeans of a syringe. After a few minutes, the metal had already turneddark; after 20 hours of stirring, a black suspension had formed. Thesolid formed was isolated using a Schlenk frit under protective gas(argon).

Yield: 0.61 g

An X-ray diffractogram showed that the black solid contains the phasesLiH and Al.

EXAMPLE 2 Preparation of Active Lithium Hydride LiH* from LiAlH₄ andLithium Powder in Et₂O

In a glass flask rendered inert (i.e., heated and filled with argon),0.29 g (41.8 mmol) of lithium powder (D₅₀=approximately 80 μm) weresuspended in 45 mL of dry diethyl ether. Then, 13.9 mmol of LiAlH₄ inthe form of an approximately 12% solution in diethyl ether were added bymeans of a syringe. After a few minutes, the metal had already turneddark; after 20 hours of stirring, a black suspension had formed. Thesolvent was removed by condensation under a vacuum. A powdery,pyrophoric residue remained.

Yield: 0.65 g

An X-ray diffractogram showed that the black solid consists of thephases LiH and Al.

EXAMPLE 3 Preparation of Active Sodium Hydride NaH* from LiAlH₄ andSodium Powder in THF

In a glass flask rendered inert (i.e., heated and filled with argon),0.96 g (42 mmol) of sodium powder were suspended in 43.7 g of drytetrahydrofuran. Then, 14.5 mmol of LiAlH₄ in the form of anapproximately 10% solution in tetrahydrofuran were added by means of asyringe under magnetic stirring. After stirring for approximately 3hours at RT, the metal turned dark. After a reaction time of 20 hours,the stirrer was turned off, a sample was removed from the upper liquidregion, filtered until clear through a membrane syringe filter (0.45 μm)and examined for dissolved hydride activity (by gas volumetry). In thecase of decomposition in water, the clear filtered sample developed nosignificant gas volume, i.e., the soluble AlH4 had been convertedlargely completely to insoluble NaH* and Al.

The black solid formed was isolated and dried.

Yield: 1.32 g (87% of the theory)

Analysis (ICP): Na=27 mmol/g; Al=9.1 mmol/g; Li=9.1 mmol/g X-raydiffractometry:

Sodium hydride, aluminum metal (main products)

Sodium metal, Na₂LiAlH₆ (secondary components)

EXAMPLE 4 Preparation of Highly Active LiH* and Addition to B(sec-Bu)₃

In a glass flask rendered inert (i.e., heated and filled with argon),0.31 g (44.7 mmol) of lithium powder (D₅₀=approximately 80 μm) weresuspended in 20 mL of dry tetrahydrofuran. Then, 13.9 mmol of LiAlH₄ inthe form of an approximately 10% solution in tetrahydrofuran were addedby means of a syringe. After a few minutes, the metal had already turneddark; after stirring for 20 hours, a black suspension had formed.

Then, 43.6 g (55.7 mmol) of B(sec-Bu)3 in the form of a 1 M solution inTHF were added within 15 minutes (min) at room temperature. A slighttemperature increase (approximately 30-35° C.) was observed. At certaintimes, solution samples were collected, immediately filtered until clearby means of a membrane filter and examined by ¹¹B NMR spectroscopy:

Reaction time B species content, % 1 hour 5 hours 23 hoursLi[HB(sec-Bu)₃], doublet 79 85 92 δ¹¹B = −5.2 ppm B(sec-Bu)₃, 21 15 8δ¹¹B = 85 ppm

EXAMPLE 5 Preparation of Highly Reactive LiH* and Addition toR-13-isopinocampheyl-9-borabicyclo[3.3.1]Nonanes, R-Alpine-Borane

In a 100-mL ISO threaded bottle rendered inert (i.e., heated and filledwith argon) with septum closure, 0.155 g (22.3 mmol) of lithium powder(D₅₀=approximately 80 μm) were suspended in 30 mL of drytetrahydrofuran. Then, 7.1 mmol of LiAlH₄ in the form of anapproximately 10% solution in tetrahydrofuran were added by means of asyringe. Already after a few minutes, the metal had turned dark; after20 hours of stirring, a black suspension had formed. Then 4.78 g (27mmol) of R-Alpine-Borane in the form of a 0.5 molar solution in THF wereadded within 30 min by means of a syringe/syringe pump. Spontaneousheating (in the end approximately 40° C.) was observed. A sample of thereaction mixture was filtered until clear and examined by ¹¹B NMR.

Alpine-Borane (δ¹¹B=85.3 ppm): not detectable, thus completely reacted

LiH addition product (δ¹¹B=−5.4 ppm, doublet): approximately 100%

EXAMPLE 6 Preparation of Highly Active LiH* with Catalytic LiAlH4Quantities

0.284 g (40.9 mmol) of lithium powder (D₅₀=approximately 80 μm) werefilled into a glass flask which had been rendered inert (i.e., heatedand filled with argon). The flask was evacuated twice and aerated withhydrogen gas. Via a hose, a connection to a graduated hydrogen reservoirwas established. Then, 24.5 g of dry tetrahydrofuran and 2.20 mmol ofLiAlH₄ in the form of a THF solution were added. Slow magnetic stirringwas carried out at RT. After approximately 2 h, the lithium powder hadturned black, wherein the consumption of hydrogen gas had started. After20 hours of stirring, 529 mL (20.2 mmol) of hydrogen had been absorbedfrom the suspension. This consumption corresponds to 99% of the theory.

The solid formed was isolated using a Schlenk frit.

Yield: 0.29 g

An X-ray diffractogram showed that the black pyrophoric solid containsthe phases LiH and Al/Li alloy.

EXAMPLE 7 Preparation of Active Aluminum from Triethylaluminum andLithium Metal

0.97 g (140 mmol) of lithium powder (D₅₀=approximately 80 μm) werefilled into a glass flask which had been rendered inert (i.e., heatedand filled with argon). 20 mL of toluene were added, and subsequently,using the canula technique, 187 mmol of triethylaluminum in the form ofa 25% solution in toluene were added within 30 min. Stirring was carriedout for 5 hours at room temperature. In the process, a black dispersionformed. The reaction mixture was filtered, and the black filter residuewas dried in a vacuum.

Yield: 0.87 g (69% of the theory, black powder)

An X-ray diffractometric examination showed that it was Al metal.

The filtrate was examined by ²⁷Al NMR:

δ=155.9 ppm, h_(1/2)=300 Hz (characteristic for LiAlEt₄)

1. Highly reactive mixtures of alkali metal or alkaline earth metalhydrides MH_(n)*, where n=1 or 2 corresponding to the valence of themetal M, and highly reactive metal M²* selected from the groupconsisting of B, Al, Ga, In, and optionally with another metal hydrideM¹H_(m)* with M¹ selected from an alkali metal, an alkaline earth metalor an element from the group of the rare earths, wherein the molar ratiobetween MH_(n)*, M²* and M¹H_(m)* is 1:0.001 to q/6:0 to p/6, preferably1:0.01 to q/6:0 to p/6.
 2. The mixtures according to claim 1,characterized in that M and M¹ are selected from Li, Na or Mg, andM²=Al.
 3. A method for preparing highly reactive alkali metal oralkaline earth metal hydrides MH_(n)* where n=1 or 2 corresponding tothe valence of the metal M, characterized in that metals M of the firstor second periods of the periodic table of elements are reacted with acompound of general formula M¹ _(x)[M₂H_(3+x)]_(b) under inertconditions or under hydrogen atmosphere according toM+o/6M ¹ _(x) [M ₂ H _(3+x)]_(b) −−>MH _(n) *+p/6M ¹ H _(m) *+q/6 M ²* ,wherein M¹=an alkali metal selected from the group consisting of Li, Na,K, Rb, Cs, an alkaline earth metal selected from the group consisting ofBe, Mg, Ca, Sr, Ba; x=0 or 1, M²=an element of the 3rd main group of theperiodic table of elements selected from the group consisting of B, Al,Ga, In; b=the valence of M¹; m=1 or 2, corresponding to the valence ofthe metal M¹; n=1 or 2, corresponding to the valence of the metal M; andin the case in which x=0, p=0, and for M=alkali element, o and q=2; forM=alkaline earth element, o and q=4 and in the case in which x=1: for Mand M¹=alkali metals, o, p, q=2; for M and M¹=alkaline earth metals, o,p=2, and q=4; for M=alkali metal and M¹=alkaline earth metal, o, p=1,and q=2, and for M =alkaline earth metal and M¹=alkali metal, o, p, q=4.4. A method for preparing highly reactive alkali metal or alkaline metalhydrides MH_(n)* where n=1or 2 corresponding to the valence of the metalM, characterized in that metals M of the first or second period of theperiodic of table of elements are reacted with a compound of generalformula M¹ _(x)[M²(A¹ _(y)A² _(z))_(3+x)]_(b) or in the presence offinely dispersed, highly reactive metal M²⁺ with a mean particle sizeD₅₀ in the range from 0.01 to 100 μm in the presence of hydrogen gas oranother source of hydrogen according to

wherein M¹=an alkali metal selected from the group consisting of Li, Na,K, Rb, Cs, an alkaline earth metal selected from the group consisting ofBe, Mg, Ca, Sr, Ba, or an element from the group of the rare earthsselected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, Lu; x=0 or 1; n=1 or 2, corresponding to thevalence of the metal M; b=the valence of M¹; M²=an element of the 3rdmain group of the periodic table of elements, selected from the groupconsisting of B, Al, Ga, In; A¹=H or an alkyl group, branched orunbranched, containing 1-18 C atoms, wherein the up to four A groups canbe identical or different; A²=an alkoxy residue OR where R=alkyl with1-8 C atoms, a dialkylamino residue —NR₂ where R=alkyl with 1-8 C atomsor a halogen from Cl, Br, I; y can assume the value 1, 2 or 3, andwherein y+z=3.
 5. The method for producing highly reactive metalhydrides MH_(n)* according to claim 3 or 4, characterized in that thereaction is carried out in an aprotic solvent or solvent mixture,wherein at least one of the solvent components is an open-chain orcyclic ether, a tertiary amine or a hydrocarbon, either in pure form oras any mixtures of at least two of the listed solvents.
 6. The methodaccording to claim 5, characterized in that an open-chain or cyclicether selected from the group consisting of diethyl ether,1,2-dimethoxyethane, diethylene glycol dimethyl ether, tetrahydrofuran,2-methyl tetrahydrofuran, tetrahydropyrane, dioxane, dioxolane; atertiary amine selected from the group consisting of triethylamine,tributylamine, morpholine, or a hydrocarbon selected from the groupconsisting of saturated C₄-C₁₈ hydrocarbons, preferably pentanes,hexanes, heptanes, octanes; aromatic compounds selected from the groupconsisting of benzene, toluene, ethylbenzene, xylenes, cumene.
 7. Themethod according to claims 3 to 6, characterized in that the reactiontemperature is in the range between −20 and 150° C., preferably 0 and100° C., and particularly preferably between 25 and 70° C.
 8. The methodaccording to claim 4, characterized in that one operates under H₂atmosphere, wherein the H₂ pressure is between 1 and 300 bar,particularly preferably 10-100 bar.
 9. The method according to claim 4,characterized in that the compound M¹ _(x)[M²(A¹ _(y)A² _(z))_(3+x)]_(b)is used in catalytic quantities from 0.001 to 20 mol %, preferably from0.01 to 10 mol %, with respect to the metal M.
 10. The use of the metalhydrides MH_(n)* according to claim 1 or 2 or obtained according to oneof claims 3 to 8 for the reaction with Lewis acids of the 3rd main groupof the periodic table of elements or for the hydrometalation of olefins.11. The use according to claim 10 for the preparation of metalhydridoborates M[HBR₃]_(n) or metal hydridoaluminates M[HAI(OR)₃]_(n)with R=unbranched, cyclic or branched alkyl groups containing 1 to 12 Catoms.
 12. The use according to claim 10, characterized in that a Lewisacid is selected from the group consisting of tri-sec-butylborane,trisiamylborane, tricyclohexylborane, aluminum trimethylate,aluminum-tri(tert-butylate), aluminum tri(tert-pentylate).
 13. The useaccording to claim 10 for the hydrometalation of an olefin R¹R³C═CR²R⁴where R¹, R² and R³=H, wherein preferably an a-olefin from the groupconsisting of 1-propene, 1-butene, 1-pentene, 1-hexene, 1-heptene,1-octene is selected.
 14. The use according to claim 10 for thehydrometalation of an olefin R¹R³C═CR²R⁴ where R² and R⁴=alkyl groupscontaining 1-12 C.